Sheet for electrical inscription



Patented May 4, 1954 2,677,651 SHEET FOR ELECTRICAL INSCRIPTI-ON HomerJ. Dana. and Raymond L. Albrook, Pullman, Wash., assignors to StateCollege of Washington, Pullman, Wash.

No Drawing. Application October 9, 1950, Serial No. 189,282

11 Claims. 1

Th present invention relates to inscription of information upon sheetsby electric current. In particular the invention relates to facsimilesheets upon which inscription is made by the receivin and recording unitof a facsimile transmission system. In the field of facsimiletransmission in particular, the requirements to be met in theinscription of a received message are quite varied and severe. It isnecessary that the affected parts of the record sheet show adequatecolor contrast, when compared with the unaffected parts, for legibility.Preferably the contrast should be suffioient to permit use of the sheetfor retransmission of the message thereon.

There are several different kinds of sheets in present day use forfacsimile reception. To the best of our knowledge, however, these sheetsdo not meet the several requirements in a satisfactory manner. It isdesirable that the record receiving sheets be of such a nature that theymay be stored dry and remain relatively unaffected by humidity changes.The sheets should be usable in the dry state and should not requireprocessing beyond actual reception of the electrical impulses. It ishighly desirable to avoid any sparking in the electrical inscription asthis limits the use of the sheets to exclude any particular area wherethere may be xplosive fumes such as exist in an aircraft when there is agasoline leak. The record sheet must be capable of withstanding widevariations in altitude and must be usable in a temperature range fromabout 60 degrees F. to 130 degrees F. The sheet must be non-toxic andshould be stable for a period of at least three or four months.

It is th purpose of the present invention to provide a record sheetwhich is stable in the temperature range and for the period set forthabove, capable of being inscribed by passing electric current through.it, wherein the sheet embodies a compound which reacts chemically withanother material toproduce change in color, and, an electricallyconductive impregnation which is changed by the passage of current, toproduce, at the point of current passage, the other material necessaryto effect a color change in the sheet, the color producing compound andthe electrically conductive impregnating material being of such a naturethat prior to the activation by the electriocurrent, they can both beintimately mixed through the body of the sheet and remain stable underthe conditions set forth in the preceding paragraph.

More particularly the present invention consists of combining, in areception sheet for electrical inscription, a solution of asubstantially colorless basic salt of nitric or nitrous acid in asolvent which will not freeze within the temperature limitationshereinbefore set forth and which evaporates very slowly; and a Betanaphthyl amine compound which will react chemically with theelectrolytic decomposition products of the aforesaid salt to form avisible color contrast to the sheet. The Beta naphthyl amine compounds,which react chemically in the aforcgoing fashion, are best described aselectro-chromotropic compounds to distinguish them from compounds whichmay be eleotro-sensitive but do not produce a visible inscription in thesheet.

It is evident that the sheet, in order to be useful in the presentelectrical transcription of messages must respond quickly to the passageof electrical imp-ulses through it. The customary methods of electricalinscription in facsimile reproduction pass the current through the sheetat spaced spots to create dots which when completed show theinscription. These dots are currently formed at a rate as high as onedot at millisecond. The time is short in which to effect the necessaryelectrolytic decomposition and the reaction of the decompositionproducts with the electro-chromotropic compound.

The electro-chromotropic compounds are not necessarily conductive, but,if sparking is to be prevented the sheet must have relatively highconductivity. Accordingly we prefer to employ a relatively thin andsmooth sheet so that the stylus or other contacting element may rideclosely upon the sheet without bouncing. Also the very thinness of thesheet itself, reduces the resistance to current flow and lessens the pos'sibility of sparking. Various sheets have been found to he sufiicientlysmooth and thin. Linen cloth used for making tracing cloth has been usedsatisfactorily. A very fine weave cotton cloth has also been usedsatisfactorily. Various papers may also be used. The color of the sheetis not too critical although white is preferable because a white background fits in so Well with the various photographic reproductionprocesses and gives maximum contrast to the colors produced by passingelectrical current through the sheet.

The manner of making the sheet conductive to electrical current israther critical. The conductivity should not change appreciably over therange of temperature (-60 degrees F. to 136 degrees l t). Furthermorethe conductivity should remain substantially constant over a long periodof time. It is essential that the conductivity be uniform throughout theused area. The electrolyte used must be impregnated into the sheet witha particular solvent in order to avoid freezing or absorption over thetemperature range and for the desired life period. Satisfactory solventsare those with low vapor pressures and low freezing points such aspolyhydroxy alcohols, derivatives of polyhydroxy alcohols, andpolymerized polyhydroxy alcohols. These solvents should remain liquidover the temperature range limitations. Specific examplesof ,the aboves01- vents are the following: Ethylene glycol (CHzOI-I) 2 glycerinCI-IOH CH2OH)2, propylene glycol' CI-IsCI-IOH CHzOI-l', diethleneglycolHOCHzCI-IzOCI-IzCI-IzOH and triethylene glycol HOC2I-I4OC2H4OC2H4OH.

Higher molecular weight polyhydroxy alcohols,

"theiresters and polymerized products are not suitable solvents. Suchsolvents do no permit either sufficient solubility 'or ionization of theelectrolytes for the necessary conductivity. For example, the followingsubstances are unsatisfactory as solvents :-mannitol, sorbitol,carbutoxytetraglycol, dimethoxytetraglyool, ethylene glycol monomethylethenpolyglycol P-400 and poly glycol -P-"750.

The solvent just described contains, in solu- .tion, and at leastpartially ionized, a stable ni- :trate.salt characterized by absence of,or very low color. When the sheets are impregnated with the solvent andsalt they remain conductive even whendry'in the usual sense. In generalthe steps .of making the sheets conductive are carried out by passingthem through a bath of equal parts of water and glycerine in which astable nitrate such asammonium nitrate is dissolved. Excess liquid isremoved by passing the sheet between rolls under light tension. Thesheet is dried by passing it over heated rolls to remove the excesswater. The paper is dry to the touch and can bestored or used. Theelectrical resistance is of :the order of 30 ohms to 100 ohms.

The nitrate salts which are suitable for this purpose are those whichare colorless or of very low color. They are retained in solution by thepolyhydroxy alcohol solvents throughout the temperature range of 60degrees F. to 130 F. They do not of themselves change color underexposure to light. The preferred salt is ammonium nitrate, or sodiumnitrite. Examples of salts that are satisfactory are the nitrates andnitrites of sodium, potassium and zinc, and nitrate. Nitrate salts ofcopper and chromium are not satisfactory because they are highlycolored. Strontium and barium nitrates can be dis solved in the waterand then the glycerine or other softener may be added. Both of the abovenitrates give good results.

The essential characteristics of the salts are thatthey are soluble inthe solvent. readily conductive, of very low color, and that theydecompose readily when current is passed through the sheet.

The sheets are impregnated with a compound which becomes reactive withthe electrolyte in solution'in the sheet, only upon the passage ofcurrent, to produce a visible color change. The compounds having thischaracteristic we term electro-chromotropic to distinguish them fromcompounds which are electro-sensitive. under like conditions, withoutvisible change in color. These compounds do not react with the nitratesalts in the sheet in the absence of the passage of electric current.The compounds are of the Beta naphthyl amine type. B-naphthylderivatives of n-alkyl diamines up to and including hexamethylenediamine have been found to mark. Those above the hexamethylene diaminemay be disregarded as :the marking value is not sufficient for practicaluse. We 'flnd that all'B-naphthyl amine derivatives not capable offorming quinoid structures by oxidation may be disregarded. For example,tribetanaphthylmelamine is not satisfactory. The'following particularcompounds are illustrativeofoperative B-naphthyl amine derivatives N,Ndi-B-naphthyl-p-phenylene diamine iPhenyleB-naphthyl amine Di-Z-naphthylamine N,N di-B-naphthyl benzidine N,N di-B-naphthyl ethylene diamine N,Ndi-B-naphthylpropylene diamine This class of compounds reacts Withelectrolytic decomposition products of nitrates "or nitrites to formoxidized, nitro or nitros'o compounds.

Probably all three types of reaction take place during electro-chemicalreactions at the stylus or wheel contact. Such reaction products arecolored ranging from light gray to black and from light yellow or brownto dark brown depending upon the amount of current flowing-through'thepaper or cloth. Introduction of a small amount of metal from thestylus:or Wheel, though not essential for color change, will catalizethe reaction and will affect .the amount of andintensity of colorproduced, an iron stylus or wheel will produce brown colors, one ofcopper will produce gray or black and aluminum produces a greenishcolor.

B-naphthyl amine compounds in water suspension can be oxidized, nitratedor sulfonated by adding appropriate reagents. Such compounds vary fromgreen to black depending upon concentration of oxidizing, nitrating or'sulfonating agent. This proves that the metal of the stylus is notnecessary for color formation. The color produced from such compoundsasphenyb B-naphthyl amine, di-2-naphthyl amine, N,N di- IB-naphthylethylene diamine and 'N,N di-B- naphthyl propylene diamine is lightyellow to 'light brown which results from formation of nitro-' andnitroso-reaction products at the stylus. The dark brown to black colorfrom such compounds as N,N di-B-naphthyl-p-phenylene diamine and N ,Ndi-B-naphthyl benzidene results from quinoid structure formation byoxidation from reaction products at the stylus.

The above named'class of compounds are not water soluble. Solubilitywill vary with solvents used. .Ethyl alcohol, acetone, pyridine,picoline, xylene, morpholine, thio-diglycol and other solvents "may beused. Pyridine and the picolines have been found to be'best for makingsolutions of the B-naphthyl amines as the solubility is greater in thesetwo specified solvents than in some of the others named.

Solutions of one-half of onepercent /2 of 1%) to maximum of thesolubility of the B-naphthyl amine compound in the solvent have beenused to impregnate paper or cloth. Excess solution is then removed bypassing the treated paper or cloth between compression rubber rolls. Bychanging the pressure'of the rolls the amount of solution left in thepaper or cloth can be varied. After the solvent is evaporated the paperor clothis treated with a solutionof-electrolyte, solvent and water tomake the paper or cloth conductive. The B-naphthyl amines are insolublein such solutions and therefore the compounds remain distributed on thefibres of the cloth or paper. Excess conductive solution is removed bypassing the paper or cloth between compression rubber rolls. Quantity ofthe conductive solution (electrolyte, solvent and water) left in thepaper may be varied by the pressure of the rolls. After drying to removeexcess Water left in the paper or cloth after passing between thecompression rolls the paper or cloth is ready for use.

To improve adhesion of the B-naphthyl amine compounds to paper and clothfibres such fibre may, though it is not absolutely essential, bepretreated by saturating with a solution of Lead acetate (Pb(Ac)2), zincacetate (Zn(Ac)z), Aluminum acetate (Al(Ac): or other mordants. Zincacetate is preferabl: due to higher solubility than Aluminum acetate andits relatively low toxicity. Sulfonated alcohols or fatty acids may beused in small amounts to lower surface tension and obtain betteradhesion and distribution of B-naphthyl amine compounds over the surfaceof the fibres.

Another method for applying the B-naphthyl amines to the fibre of paperor cloth is to dissolve the electro-chromotropic compound in pyridine,morpholine, thio-diglycol or other solvent which is miscible with water,saturate the paper or cloth with the solution and, Without driving 01for evaporating the solvent, passing the paper through a water bath.Excess water will precipitate the B-naphthyl amine from the solvent uponthe fibres of the paper or cloth.

Example A.Four and onehalf (4 grams of bLN di-B-naphthyl-p-phenylenediamine are dissolved in 66 ml. pyridine. Paper or cloth previouslydescribed is immersed in the solution until thoroughly saturated thenpassed between rolls which have very light tension. The solvent ispermitted to evaporate at room temperature or may be passed over a sheetof aluminum heated by a hot plate. the paper or cloth is passed througha bath of 11 grams of ammonium nitrate, 17 grams of glyocrine and 17grams of water. Excess liquid is removed by very light tension on therolls. Ex-

cess water is removed by passing the paper over heated rolls. The paperis ready for inscription or may be stored for future use.

Example B.-Paper or cloth may be pretreated by soaking in a watersolution of 5% zinc acetate and dried. After drying the paper is thentreated in the same steps as used in Example A.

Example C.-Nine (-9) grams of phenyl-B- naphthyl amine are dissolved in66 ml. pyridine. Unpretreated or pretreated paper is saturated with thissolution and excess solution removed by rolls. After the solvent hasbeen evaporated the paper is saturated with a solution of 9 grams ofammonium nitrate, 14 grams of glycerine and 17%; ml. of water. Afterremoving excess water by drying the paper is ready for inscription.

Example D.Picoline is substituted for pyridine in Example A.

Example E.-Glycol or diethylene glycol is substituted for glycerine inExample A.

The beta naphthyl amine compounds are insoluble in Water and quitestable. They can be incorporated into the sheet in different ways. Theymay be dissolved in pyridine, morpholine, or thio-diglycol and appliedto the sheet. The sheet is then immediately passed through water.

After the solvent is evaporated 6 l The beta naphthyl amine compoundsare precipitated on the sheet fibers and the solvents, being themselvessoluble in water, are drained out.

A. solution of the Beta naphthyl amine group in pyridine can be added tothe paper pulp beater to precipitate the group on the pulp fibers. Whenthe paper is formed the beta naphthyl precipitate will be in the matrixof the paper.

Sheets treated in accordance with the foregoing disclosure may beinscribed by the usual facsimil equipment with voltages as low as volts.Higher voltages up to 280 volts have been used without sparking. Eitheralternating or direct current may be used but an anodic stylus willeffect the greatest density of color. The color change is mostpronounced at the anode surface of the sheet. When alternating currentis used alternate dots on the stylus side of the sheet will be missingor less visible because of current reversal. Direct current is thereforepreferable. I The preferred electro-chromotropic compound is N,Ndi-B-naphthyl-p-phenylene. Our experiments have shown it to give thegreatest color contrast between the inscription and the surroundingsheet surface. If a sheet is impregnated with this compound and theelectrolyte ammonium nitrate, the sheet is slightly gray. The contrastbetween the inscription and the surrounding area is great enough forblue-printing or retransmission. The sheets are stable.

It is believed that the nature and advantages of our invention will beapparent from the foregoing description. i-Iaving thus described ourinvention, we claim:

1. A substantially dry sheet adapted for visible inscription by passageof electric current therethrough comprising a non-conducting base ma--terial impregnated with a solution of substantially colorless nitrate ina polyhydroxy alcohol and with a water insoluble organic compound havinga Beta naphthyl amine radical and capable of forming quinoid structuresby oxidation, said organic compound being capable of being oxidized insitu upon decomposition of said nitrate by passage of current throughthe sheet.

2. A substantially dry sheet adapted for visible inscription by passageof electric current therethrough comprising a non-conducting basematerial impregnated with a water insoluble organic compound having aBeta naphthyl amine radical and. capable of forming quinoid structuresby oxidation and with a solution of a substantially colorless basic, aninorganic salt from the group consisting of nitrates and nitrites in apolyhydroxy alcohol of the group consisting of ethylene glycol,glycerine, propolene glycol, diethylene glycol and triethylene glycol,said organic compound being capable of being oxidized in situ upondecomposition of said inorganic salt by passage of current through thesheet.

3. A substantially dry sheet adapted for visible inscription by passageof electric current therethrough comprising a non-conducting basematerial impregnated with a water insoluble organic compound having aBeta naphthyl amine radical and capable of forming quinoid structures byoxidation and with a solution of ammonium nitrate in a polyhydroxyalcohol of the group consisting of ethylene glycol, glycerine, propoleneglycol, diethylene glycol and triethylene glycol, said organic compoundbeing capable of being oxidized in situ upon decomposition of saidnitrate by passage of current through the sheet.

4. A substantially dry sheet adapted for visible inscription why passageof electric current 'LthEI'G- through "comprising a non-conducting'sheet of fibrous material impregnated with a water in- :solube'organiccompound having a Beta naphthyl amine "radical and capable of formingquinoid structures by oxidaticn-and with asolu- :tion of a substantiallycolorless basic, an inorganic salt from thegroup-consisting'of nitratesand ,nitrites in .a polyhydroxy alcohol of the group consisting ofethylene glycol, glycerine,

;propolene glycol, 'diethylene glycol "and triethyl- :ene glycol,said:organic'compound being-capable of being oxidized in situaupondecomposition of saidinorganic :salt by;passage ,of currentithrough thesheet.

5. A substantially dry sheetadapted for visible inscriptionby passageof-electric current therethrough comprising anon-conducting paperimpregnated with a Waterinsoluble organic compound having aBetatnaphthyl amine radical and capable of 'formingquinoid structures byoxidation and Wl'ChTasolution of ammonium nitrate in aypolyhydroxyalcohol oithe group consisting of ethylene glycol, -.glycerine,propolene glycol, diethylene glycol and triethylene glycol, said organiccompoundbeing capable of being oxidized in'situ upon decomposition ofsaid nitrate by passage of current through the sheet.

6..A substantially dry sheet adapted for visible inscription bypassage'of electriccurrent there-- through comprising :a non-conductingsheet of fibrous material, having-a water insoluble organic compoundhaving a Beta naphthyl amine radical and capable of forming quinoidstructures by oxidationdistributedthereon, said sheet containing asubstantially-colorless solution of: an inorganic salt from .the groupconsisting of nitrates and nitrites in glycerine, said organiccompoundbeing capable of being oxidized. insitu upon decomposition ofsaidinorganic salt by passage of current throughthe sheet.

7. A substantiallydry sheet adapted for visible inscription by passageof electric current there- 'through comprising a non-conducting sheet offibrous material, having N,N di-beta-naphthylp-phenylene .diaminedistributed thereon, said sheet containing a substantially colorlesssolutionof an inorganic salt of nitrogen. in glycerine, said diaminebeing capable of being oxidized in eitu upon decomposition of saidinorganic salt bypassageof current through the sheet.

8. A substantially dry sheetadapted for visible inscription by passageofelectric current there- .through comprising a non-conducting sheet offibrous niaterial,.having N,N -di-beta-naphthylpephenylene diaminedistributed thereon, said sheet containing a solution of ammoniumnitrate .in glycerine, said diamine being-capable of being oxidized insitu upondec-omposition of said nitrate by passage-of current throughthe sheet.

-9. A substantiallydrysheet adapted for visible inscription by passageof electric currenttherethrough comprising a non-conducting sheet 'offibrous material, having N,N di-beta-naphthyl-rp-phenylenevdiamineuniformly distributed therein,-said sheet containing asolution ofammonium nitrate in glycerine, said diamine being capable ofbeing'oxidized in situ upon decomposition of said nitrate by passage ofcurrent through the sheet.

10. A substantially dry sheet adapted for visible inscription by passageof electric current .tlierethroughcomprising a non-conducting sheet offibrous-materiaLhaving a Water. insoluble organic compound having a Betanaphthyl amine radical and capableotforming quinoid structures .byoxidation distributed thereon, said sheet conpound having aBetanaphthylamineradical and capable of forming .quinoid structures by oxidationdistributed thereon, said sheet containing a substantially colorlesssolution of an in organic salt from the group consisting of nitratesand-nitrites .in apolyhydroxy alcohol-of the group consisting ofethylene glycol, glycerine, propylene glycol, vdiethylene glycol andtriethylene glycol; said organic compound being capable of beingoxidizedin situ upon decomposition of said inorganic salt by. passage ofcurrent through the sheet.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 168,466 Edison Oct. 5, 1875 670,510 Friese-Greene Mar. 26,1901 2,229,091 Kline Jan. 21, 1941 2,281,013 Talmey Apr. 23, 19422,346,670 Engler et al Apr. 18, 1944 2,459,521 Greig Jan. 18, 19492,513,238 Greig June 27, 1950 OTHER REFERENCES Electrolytic Oxidationand Reduction, Glassstone and Hickling, 1936, pages 318-328.

Electra-Organic Chemistry, 1926, pages 11 121, by Brockman.

I-Iackhs Chemical Dictionary, 3d edition, 1944, page 259.

Websters New. Int. Dictionar', 2nd edition, 1940. page 704.

1. A SUBSTANTIALLY DRY SHEET ADAPTED FOR VISIBLE INSCRIPTION BY PASSAGEOF ELECTRIC CURRENT THERETHROUGH COMPRISING A NON-CONDUCTING BASEMATERIAL IMPREGNATED WITH A SOLUTION OF A SUBSTANTIALLY COLORLESSNITRATE IN A POLYHYDROXY ALCOHOL AND WITH A WATER INSOLUBLE ORGANICCOMPOUND HAVING A BETA NAPHTHYL AMINE RADICAL AND CAPABLE OF FORMINGQUINOID STRUCTURES BY OXIATION, SAID ORGANIC COMPOUND BEING CAPABLE OFBEING OXIDIZED IN SITU UPON DECOMPOSITION OF SAID NITRATE BY PASSAGE OFCURRENT THROUGH THE SHEET.